Rock drilling utilizes a rock drilling apparatus comprising a carrier, a feeding beam and a rock drill moved with respect to the feeding beam. The rock drill comprises a percussion device for delivering impacts on a tool connected to the drill, and a rotating device for rotating the tool. The rock drill further comprises means for guiding a flushing agent into a drill hole for flushing drill cuttings out of the hole. Operating parameters of rock drilling include impact pressure, feed pressure, rotation pressure medium flow and flushing pressure, which are adjusted in order to control the operation of the drilling apparatus as desired. In a widely used control arrangement the aim is to provide the drill bit with a maximum penetration rate. This arrangement comprises measuring the penetration rate of the drill bit and empirically adjusting individual operating parameters to achieve the highest possible penetration rate. The aim of another generally used control arrangement is to optimize transfer of energy from the drill to the rock. This arrangement comprises measuring the rotation power and/or rotation torque of the drill bit and keeping the variables in predetermined limits by adjusting individual operating parameters.
A disadvantage of the prior art methods is that when the operator is adjusting individual operating parameters, he/she cannot perceive the effect of the adjustment measures to the entire drilling situation and the total costs of drilling. Therefore it is very difficult to optimize drilling by adjusting individual absolute values. Adjustment of a single drilling parameter affects positively certain target criteria representing the success of drilling, but it can simultaneously affect other target criteria negatively. For example, an increase in impact power expedites drilling and thus reduces the costs of drilling, but unfortunately the service life of the drilling equipment simultaneously decreases, which in turn adds considerably to the costs of drilling. In all, in the present systems successful adjustment and control of a drilling situation is highly dependent on the experience and skills of the operator.